To keep from getting getting sidetracked, I opened a new thread on mounting packard shutters on the front of a lens here...

Back on topic...

Here's an example of using a front objective from some whopper binoculars.
It's about 350 mm focal length achromat, about 80mm diameter.
In this case I used the barrel from the binoculars, no need to make a mount.
Aperture rings are held on with a Haagen-Dazs ice cream carton rim.

It puts an image on the ground glass quite like Jim's photo of the toy car.
Nice, but I prefer the character of the meniscus for portraiture.